The invention relates to a method for the surface modification of products made of low-energy synthetic fibres, to the products produced by the method and to the use of the products produced by the method.
The term “synthetic fibres” as it is used here refers to linear, thread-like macromolecules which, for example, can belong to the material classes of aramids, polyesters, polyamides, polyacrylates, polyacrylonitriles, polyurethanes, (per)fluorinated polyolefins, such as polytetrafluoroethylene or polyvinylidene(di)fluoride, polysulfones, polyimides, polyolefins etc., as well as co- or terpolymers thereof.
In the following the term “products made of low-energy synthetic fibres” refers to molded articles in 1 and/or 2-dimensional form. Articles in 1-dimensional form include, for example, filaments, monofilaments, multifilaments, fibres, threads, yarns, strings, rovings etc. Their diameter can be in the lower μm range or in the lower mm range, for example at 6 μm on the one hand or 3.4 mm on the other hand. The length can be in the mm range (staple fibres) or in the km range (filaments). The cross section of the fibres can be round, elliptical, triangular, rectangular, polygonal, star-shaped, lobular, cylindrical etc. The unmodified fibre surface may be rough or smooth. In mainly 2-dimensional form these are textile materials which exist as filament composite material such as tissue, knitted fabrics, fleece, nets, braids etc. or as fibre composite material such as non-wovens, felts, wadding etc. or as combinations of filament and fibre composite materials such as textile multilayer composites.
The area density is limited only by the technical feasibility and can range, for example, from 6 g/m2 to 1,600 g/m2. In particular in connection with surface modification(s), the term “material” is also used in the following for the abovementioned products made of synthetic fibres.
The term “surface modification” used here means that the surfaces of non-surface-modified materials differ from surface-modified materials in at least one of the following features:                in the results of surface analysis using, for example, ESCA (Electron Spectroscopy for Chemical Analysis) or SIMS (Secondary Ion Mass Spectroscopy)        in the wettability with water        in the electrostatic properties        in the chemical reactivity, e.g. in the ability to be dyed with water-soluble dyes        
The term “low-energy” as used here means that products made of low-energy synthetic fibres have at least one of the following properties:                the free surface energy is less than 40 mN/m        the contact angle of water is greater than 45°, i.e. the wettability is low or absent, the material is hydrophobic        they cannot be dyed from the aqueous phase        they can easily become electrostatically charged.        
Products made of low-energy synthetic fibres, particularly those made of polyolefins, have several disadvantages:                the material surfaces are chemically inert; they have no functional groups or only functional groups that can be activated with (chemically) drastic means, so that, for example, dyeing directly from the aqueous phase is not possible.        the materials easily become electrostatically charged, which prevents any further technical use.        the materials are not wettable with water. They cannot be used as lining in garments for example, as the inability to absorb perspiration would leave the wearer sweating. They cannot be used for wound dressings/hygiene products as they cannot absorb or convey wound secretions/body fluid. They cannot be used as filter material for aqueous media as the water cannot penetrate the material.        
Solutions proposed to overcome the abovementioned disadvantages involve either finishing the surface of low-energy materials with surface-active substances such as wetting agents or surfactants, or depositing hydrophilic polymers such as polyvinyl pyrrolidone or polyvinyl alcohol on the surface. The proposed solutions are not satisfactory as the finishing with surface-active substances is not permanent; they are washed off/out on contact with water. In order for hydrophilic polymers to be retained on the surface, they have to be linked with certain substances, some of which are toxic; this is complicated and costly.